Device for producing a homogeneous beam of solid particles

ABSTRACT

The device comprises a gas-tight vessel divided into two sections by a substantially horizontal porous wall, a source of gas under pressure connected to the lower portion of said vessel in order to supply this latter with gas at an adjustable flow rate, a reservoir designed to supply powder consisting of solid particles and to communicate with the upper portion of the vessel, a duct for connecting the upper portion of the vessel to the inlet of a pumping column which consists of a plurality of gas-tight chambers in vertically stacked relation and the delivery duct of which constitutes the outlet of the device.

United States Patent Geller et al.

v [451 Feb. 11, 1975 DEVICE FOR PRODUCING A l-IOMOGENEOUS BEAM OF SOLID PARTICLES Inventors: Richard Geller, Grenoble; Francois Juillet, Bron; Paul Meriaudeau, Rillieux, all of France Assignee: Commissariat a IEnergie Atomique,

Paris, France Filed: Jan. 7, 1974 Appl. No.2 431,316

Foreign Application Priority Data Jan. 11, 1973 France 73.00882 US. Cl 250/251, 250/492 Int. Cl. H0lj 37/00 Field of Search 250/251, 492

References Cited UNITED STATES PATENTS 6/1973 Damm 250/251 3,790,787 2/1974 Geller 250/251 Primary Examiner-James W. Lawrence Assistant Examiner-C. E. Church Attorney, Agent, or Firm-Cameron, Kerkam, Sutton, Stowell & Stowell [57] ABSTRACT The device comprises a gas-tight vessel divided into two sections by a substantially horizontal porous wall, a source of gas under pressure connected to the lower.

portion of said vessel in order to supply this latter with gas at an adjustable flow rate, a reservoir designed to supply powder consisting of solid particles and to communicate with the upper portion of the vessel, a duct for connecting the upper portion of the vessel to the inletof a pumping column which consists of a plurality of gas-tight chambers in vertically stacked relation and the delivery duct of which constitutes the outlet of the device.

13 Claims, 2 Drawing Figures PATENTEI] FEB 1 1 I975 SHEEI 10F 2 PATENTED F531 1 i975 sum 2 or 2 FIG. .2

DEVICE FOR PRODUCING A HOMOGENEOUS BEAM OF SOLID PARTICLES The present invention relates to an improvement in devices for the production of a beam of solid particles. The invention finds an application primarily in the construction of devices in which beams of neutral particles or ions having multiple charges are produced by charge exchange from an ion beam, but also in studies relating to solid-radiation interactions or solid-gas reactions, or alternatively in the formation of deposits.

In US. Pat. application Ser. No. 240,947 filed Apr. 4, I972 now US. Pat. No. 3,790,787, there was described a method of production of a beam of neutral particles or multiply charged heavy ions in which electric charges are neutralized or exchanged between the charged particles of an incident beam and a substance traversed by the beam, said method being distinguished by the fact that a substantially homogeneous stream of powder of said substance consisting of grains smaller in size than 1,000 A. is caused to pass through the incident beam of charged particles in order to form a curtain which is traversed by the beam, the rate of circulation being such that either one grain or at least a number of atoms of grains correspond to each charged particle.

In the patent Application aforesaid, there was also described a device for the production of a beam of neutral particles or multiply charged heavy ions by neutralization of charged particles of an incident beam of addition of charges to said particles, said device being distinguished by the fact that it comprises means for circulating transversely to the beam a substantially homogeneous flow of powder consisting of grains smaller in size than 1,000 A. and forming a curtain, the flow rate of powder being such that a number of atoms of one grain corresponds to each charged particle.

In accordance with claim 3 of said patent application, the device is distinguished by the fact that said means for circulating a substantially homogeneous flow of powder transversely to the beam comprise a duct having its opening in a tube through which the beam passes, a supply which releases an adjustable flow of powder at the upper extremity of the' duct and means for creating a vacuum within the tube and the duct.

The object of the present invention is to provide an improvement in the means aforesaid with a view to obtaining a more homogeneous beam of solid particles, the particles being separated from each other to a greater extent and the density of the solid-particle beam being adjustable.

In precise terms, the present invention relates to a device for the production of a homogeneous beam of solid particles, wherein said device essentially comprises:

a gas-tight vessel divided into two sections by a substantially horizontal porous wall,

a source of gas under pressure connected to the lower portion of said vessel in order to supply this latter with gas at a flow rate which is adjustable by means of a valve,

a tank for supplying powder constituted by said solid particles, said supply tank being adapted to communicate with the upper portion of said vessel,

a duct for connecting the upper portion of the vessel to the inlet of a pumping column, the delivery duct of said column being such as to constitute the outlet of the device.

As a preferable feature, said pumping column is vertical and constituted by a plurality of gas-tight chambers disposed in vertical relation beneath each other, each chamber beingprovided with a feed passage which penetrates into the upper portion of said chamber, an outlet located above the extremity of the feed passage and connected to gas-pumping means, the lower portion ofa chamber being provided with an extension in the form of a delivery duct which constitues the feed passage for the following chamber. a

In claim 4 of the patent cited in the foregoing, the means for forming the powder curtain are intended to comprise an installation for giving an electric charge to the grains of powder and means whereby an electric field for accelerating the grains towards the beam is produced within a separate zone with respect to the zone through which the beam passes.

In a preferential embodiment of the device according to the present invention, there are similarly provided auxiliary means for giving an electric charge to the powder grains and means for producing an electric field for accelerating and also focusing the stream of solid particles if necessary.

The properties and advantages of the present invention will become more readily apparent from the following description relating to examples of construction which are given by way of explanation without any limitation being implied, refereence being made to the accompanying drawings, wherein:

FIG. 1 illustrates the device for producing a homogeneous beam of solid particles of adjustable density;

FIG. 2 is a diagram of the auxiliary means which serve to charge the particles produced by the device of FIG. 1 as well as to accelerate and focus said particles.

In FIG. 1, a gas-tight vessel 2 is divided into two sections 4 and 6 by means ofa substantially horizontal porous wall 8. A source 10 of gas under pressure is connected to the lower portion 4 of the vessel 2 and supplies this latter with gas through the duct 12 and the valve 14 which serve to regulate the flow rate of said gas. A tank 16 for the supply of powder consisting of solid particles which are intended to form a homogeneous beam communicates with the upper portion 6 of the vessel 2 through the duct 18 and a'cock 19. An elbowed duct 20 connects the upper portion 6 of the vessel 2 to the upper portion of a differential pumping column 22 which is constituted by a plurality of gas-tight chambers 24 disposed in vertical relation beneath each other. Each chamber 24 has a feed passage 26 which penetrates into the upper portion of said chamber, an outlet 28 located above the extremity 30 of the feed passage 26 and connected to pumping means (not shown) through the pipe 32 and a valve 33. Each chamber 24 is extended by a delivery duct which constitutes the feed passage for the following chamber. The delivery duct 36 of the last chamber constitutes the outlet of the device. An auxiliary assembly 38 can be associated with said device if necessary; the constructional arrangement of said assembly will be described hereinafter. The circuit for the utilization of the powder stream is constituted by way of example by a chamber 40 for charge exchange between a particle beam 42 and the powder stream 43. A recovery chamber 44 which is connected to pumping means through the pipe 45 serves to collect the powder which is employed and if necessary to recover this latter in order to feed the supply tank 16 once again in a cycle which is represented diagrammatically by the arrows 17. The device further comprises pumping ducts 50 and 52 at the level of the vessel 2 and the supply tank 16 for degassing the powder prior to use. Said device also comprises a duct 55 which connects the gas source directly to the top of the column 22 when the valve 54 is open. In this diagram, the connections to the pumping means (not shown) are represented schematically by the arrows P.

The operation of this device is as follows. The powder is stirred within the top portion 6 of the vessel 2 by the gas derived from the source 10 after said gas has been injected into the bottom portion 4 of the vessel and has passed through the porous wall 8. The powder is carried by the gas into the elbowed duct 20. The differential pumping column 22 makes it possible to obtain the desired residual gas pressure. The pumping outlet 28 in each chamber 24 must be located above the opening 30 for the admission of the gas-powder mixture in order to prevent the solid particles from moving upwards with the gas stream which is eliminated by pumping. The pumping circuits (not shown) therefore produce at the delivery end 36 of the column 22 a gas pressure which is adapted to the particular use ofthe powder stream. The flow rate of gas derived from the source 10 is adjusted by means of the valve 14. The density of the solid-particle beam delivered at the extremity of the duct 36 can therefore be adjusted by means of said valve 14. Prior to use, the valve 14 can be closed and degassing of the powder can be carried out through the ducts 50 and 52. The valve 54 permits operation under pulsating conditions by injection the gas derived from the supply tank 10 directly into the differential pumping column.

The device described in the foregoing makes it possible to obtain a beam of solid particles moving at a velocity which is determined essentially by the difference in pressure along the column 22, in contrast to the device described in the patent Application cited earlier which simply employed the action of gravity. The particles therefore reach the lower portion of said column at a velocity which is usually below approximately 10" cm/s in the case of installations of reasonable size. Should this velocity prove insufficient for certain applications, it is intended in the present invention to add to the base of the column 22 a device 38 which will now be described with reference to FIG. 2.

This figure illustrates the means employed for giving an electric charge to the powder grains and for producing an electric field for accelerating and focusing the grains. This auxiliary device 38 is placed between the bottom duct 36 of the last chamber of the column 22 and the device 40 for the utilization of the solid-particle beam. The device 38 comprises means 60 for giving a charge to the powder grains, means 62 for generating an electric acceleration field and means 64 for focusing the beam of charged and accelerated particles. In the example which is illustrated, the installation 60 which gives an electric charge to the powder grains comprises an annular cathode 70, an axial anode 74 which is brought to a positive potential by means of a directcurrent source 76. An electron cloud 78 is thus created between cathode and anode. The arrangement of the electrodes is such that the stream of powder passes through said electron cloud, with the result that said stream carries out electrification of the solid particles of powder within said cloud. In order that electrification through the electron cloud 78 should take place under good conditions, it is necessary to provide an electron flux of the same order of magnitude as the flux of solid particles to be electrified. The means 62 for accelerating grains thus electrified comprise a series of electrodes E E E, which are brought to positive potentials by means of a direct-current voltage source 80. The focusing means 64 are represented diagrammatically by an electrostatic lens 82 which is brought to a high negative potential by means of the source 84.

It is apparent, however, that the focusing means 64 could be of magnetic type and have windings supplied with direct current as is known to those versed in the art. Acceleration and focusing of the electrifield solid particles take place in accordance with the known laws of electron optics. However, since the mean free path of the solid particles is shorter than that'of ordinary ions by reason of the fact that their diameter is larger than that of the ions by several orders of magnitude, the vacuum within the acceleration and focusing space must have a high value of the order of 10 torr, for example. Once they have been accelerated and focused by the electric fields, the particles may subsequently loose their electric charges during collisions with the atoms of the residual gas without thereby loosing the velocity and direction which they have acquired in the system 38 which is located after the first stage described in FIG. 1. This device for accelerating and focusing solid particles makes it possible to form a continuous stream of solid particles, which was not the case with devices of the prior art for electrification of the powder, the operation of which was based on a static field generated by a system of electrodes on which the powder had been deposited.

in order to avoid heating or even decomposition of the solid particles as these latter pass through the electron cloud, these particles must be of sufficiently small size. Researches carried out by the Applicant in regard to heating of solid grains having very small dimensions by either electron or ion bombardment have shown that excessive heating of the grains is prevented if the dimensions of these latter do not exceed 300 A.

By way of example, the powder can consist of oxide grains of TiO SiO SnO or A1 0 The gas can be carbon dioxide gas (C0 The porous wall 8 can be formed of sintered glass.

What we claim is:

l. A device for the production of a homogeneous beam of solid particles, wherein said device comprised:

a gas-tight vessel divided into two sections by a substantially horizontal porous wall,

a source of gas under pressure connected to the lower portion of the vessel for supplying said vessel with gas at a flow rate which is adjustable by means of a valve,

a tank for supplying powder constituted by said solid particles, said supply tank being adapted to communicate with the upper portion of said vessel,

a duct for connecting the upper portion of the vessel to the upper portion of a pumping column, the delivery duct of said column being such as to constitute the outlet of said device.

2. A device according to claim 1, wherein said pumping column is vertical.

3. A device according to claim 1, wherein said pumping column is constituted by a plurality of gas-tight chambers disposed in vertical relation beneath each other, the chamber being provided with a feed passage which penetrates into the upper portion of said chamher, an outlet located above the extremity of the feed passage and connected to gas-pumping means, the lower portion of a chamber being provided with an extension in the form of a delivery duct which constitutes the feed passage for the following chamber.

4. A device according to claim 1, wherein said porous wall is of sintered glass.

5. A device according to claim 1, wherein said gas is carbon dioxide C0 6. A device according to claim 1, wherein said powder is constituted by at least one oxide selected from the group consisting of the oxides TiO SiO S110 and A1 0 7. A device according to claim 1, wherein said device comprises an installation for giving an electric charge to the grains of powder and means for producing an electric field for accelerating the grains.

8. A device according to claim 7, wherein said installation and said means are placed after the delivery duct of the last chamber.

9. A device according to claim 7, wherein said installation for giving an electric charge to the powder grains comprises an emissive cathode and an anode which are brought to respectively negative and'positive potentials and between which moves an electron cloud, the position of the electrodes being such that said powder passes through said electron cloud.

10. A device according to claim 9, wherein the flux of charges of the electron cloud is adjusted to the vicinity of the flux of grains of powder which passes through said cloud.

11. A device according to claim 7, wherein said means for producing an accelerating electric field are constituted by a series of annular electrodes brought to positive potentials and traversed by said electrified powder.

12. A device according to claim 7, wherein said device is provided around the beam of accelerated particles with at least one electrostatic focusing electrode which is brought to a negative potential. v

13. A device according to claim 1, wherein the solid particles constituting the powder have dimensions smaller than 300 A. 

1. A device for the production of a homogeneous beam of solid particles, wherein said device comprised: a gas-tight vessel divided into two sections by a substantially horizontal porous wall, a source of gas under pressure connected to the lower portion of the vessel for supplying said vessel with gas at a flow rate which is adjustable by means of a valve, a tank for supplying powder constituted by said solid particles, said supply tank being adapted to communicate with the upper portion of said vessel, a duct for connecting the upper portion of the vessel to the upper portion of a pumping column, the delivery duct of said column being such as to constitute the outlet of said device.
 2. A device according to claim 1, wherein said pumping column is vertical.
 3. A device according to claim 1, wherein said pumping column is constituted by a plurality of gas-tight chambers disposed in vertical relation beneath each other, the chamber being provided with a feed passage which penetrates into the upper portion of said chamber, an outlet located above the extremity of the feed passage and connected to gas-pumping means, the lower portion of a chamber being provided with an extension in the form of a delivery duct which constitutes the feed passage for the following chamber.
 4. A device according to claim 1, wherein said porous wall is of sintered glass.
 5. A device according to claim 1, wherein said gas is carbon dioxide CO2.
 6. A device according to claim 1, wherein said powder is constituted by at least one oxide selected from the group consisting of the oxides TiO2, SiO2, SnO2 and Al2O3.
 7. A device according to claim 1, wherein said device comprises an installation for giving an electric charge to the grains of powder and means for producing an electric field for acceleratinG the grains.
 8. A device according to claim 7, wherein said installation and said means are placed after the delivery duct of the last chamber.
 9. A device according to claim 7, wherein said installation for giving an electric charge to the powder grains comprises an emissive cathode and an anode which are brought to respectively negative and positive potentials and between which moves an electron cloud, the position of the electrodes being such that said powder passes through said electron cloud.
 10. A device according to claim 9, wherein the flux of charges of the electron cloud is adjusted to the vicinity of the flux of grains of powder which passes through said cloud.
 11. A device according to claim 7, wherein said means for producing an accelerating electric field are constituted by a series of annular electrodes brought to positive potentials and traversed by said electrified powder.
 12. A device according to claim 7, wherein said device is provided around the beam of accelerated particles with at least one electrostatic focusing electrode which is brought to a negative potential.
 13. A device according to claim 1, wherein the solid particles constituting the powder have dimensions smaller than 300 A. 